Dave, thanks for the explanation, it makes a lot of sense. Sounds like there are multiple ways metal can be non-recovered. That 10% figure is higher than I would have guessed. I'll be very interested to see the results of the interview, assuming you can get it.

Metal loss in melting processes is non-neglible; metal is lost due to volatilization and oxidation. The amount of loss depends on the melting process. For induction melting of steel, about 1-2% of the charge material is lost; for cupola melting of iron, the loss might be as high as 10%.

Then, not all scrap metal makes it into the recycling stream; some winds up in landfills instead. This is probably the most obvious way that material can be lost. A less obvious one is that not all scrap makes it back into the correct recycling stream. For example, steel that is mixed into aluminum scrap becomes a harmful impurity.

The statement that a given unit of steel is recycled two or three times before it is essentially lost to the recycling process is based on Markov chain modelling of the various loss processes.

One of the conclusions of the Science article is that design engineers can play an important role in increasing the effectiveness of recycling efforts. I hope to get more details about how to do this when I talk with the author.

Like Dave, I've also seen the statements about metals being "infinitely" recyclable, especially aluminum. Sad to see that for steel, recovery rates are only around 50%. But that said, Dave, what makes the piece of steel unrecoverable after 2 or 3 recycling instances? By "unrecoverable" do you mean it begins degrading, or that it becomes lost in a landfill because people don't recycle it?

'Fuels must not emit greenhouse gases. I'm at a loss for what is left.' First sentence true. Nulle desperandum. Conservation, geothermal, tidal, run of river, wind and solar for a start. Even hydro although new hydro has an appreciable carbon footprint. Existing hydro has a long way to go: recall that most hydro is ancient and that knowledge in fluid dynamics, magnetics and meteorology has gone a long way in 50 years. Many existing head ponds are capable of a technological bonus of 150 to 200%. The problem, common to most of these technologies, is simply LCOE (cost) as compared to cheap and dirty burning stuff. Even with automobiles, we can get off of gasoline now ... at a cost. By and large, we're just too cheap to save our own skins.

What I'd hope that engineers would understand, especially good product and process engineers, is that economy of scale is huge (that's the Henry Ford story): if everyone buys a product, the price will go down - a lot. For new technologies, we talk about experience curves where the cost of production decreases in proportion to cummulative quantity sold. If you would like cheap EVs, try buying 100,000,000 of them. Engineers get budget from margin which comes from sales - engineers make things better given time and money - simple equation. Experience also generates data which is invaluable - practical engineering involves a substantial amount of SPC (the good stuff is mostly bleading edge - we just call it leading edge to seem smarter).

" first-generation fuel feedstocks were chosen while ignoring their potential impact on food crops" ... no, they were not. The US policy was clearly one intended to increase the demand for corn and other grains. At the time, there was actual surplus capacity, where surplus means no market at the American price, and substantial curtailed capacity where curtailed means paying producers not to produce. 'Twasn't an accident. The option of importing inexpensive ethanol was always there. However, if it doesn't seem to make sense to an engineer, look for a politician in the works.

I'm saying that, the more often you recycle something, the more energy is used. Of course, as some point out, it's even a bit worse because of attrition - some part has to be made up of new material. Something like (1+(1-f)*(n-1))*En +f*(n-1)*Er where f is the fraction that is recycled, n is the number of lifetimes, En is the energy input for new material and Er is the energy input for recycling. Everything multiplies by n. Energy usage per unit of time is proportional to 1/Tl where Tl is the lifetime for one use and n(t) = t/Tl. Obviously, the more durable the product in which the material is used, the lower the cummulative energy input. For example, I remember when I purchased a new exhaust system for my car about every 3 years but now, even a car I've had for 10 years still needs no replacement. Ditto for front disk rotors. The energy content of the vehicle for these items is obviously easily 3 times less, even before we think about recycling. It would be ludicrous to say that recycling is not better than throwing away unless recycling takes more energy than making new material and I didn't say that.

TJ, the article states that the EC wants to increase its production of biofuel for transportation applications, but decrease the amount of feedstock that comes from food-baseed crop sources. Instead, there are several other possibilities: food crop waste (like corn husks), or non-food crop biomass (like straw). Other possible sources include non-recycled plastics, and municipal waste, all of which we've reported on.

I agree, Dave. But I think we need to remember that the reason first-generation fuel feedstocks were chosen while ignoring their potential impact on food crops happened for several reasons. We had a focus on ethanol because researchers were looking for what appeared to be the fastest, more-likely to-be-a-drop-in replacement for gasoline. We looked at corn as a source of ethanol since we, the US, have a lot of it, and here the corn lobby may be relevant, as others have mentioned. But it's also true that we looked first for a drop-in replacement, due to the economics that drive our manufacturing, instead of first seeking the "best" technology from some other standpoint, such as least harm to the environment, easiest to produce, or easiest/simplest to distribute.

George, I did a story on the steel study, and I felt a tad queasy about it simply because it was commissioned by the steel industry. Even so, the results were interesting. Like many things (including cars) improvements may come easiest by improving existing systems rather than creating new systems. Our greatest gas savings may come from improved internal combustion engines rather than hybrids or EVs.

Ann, reading your article makes me think the EU is trying to mandate magic fuels. Nuclear power is bad, fossil fuels are bad, food-based biofuel is bad. Fuels must not emit greenhouse gases. I'm at a loss for what is left.

It seems like Europe wants people to turn their skin green and photosynthesizing their own energy.

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